A non-contact position sensor disclosed in Japanese Patent Laid-Open Publication, No. H02-240585 represents one of the kinds known in the past.
A non-contact position sensor of the prior art will be described hereinafter with reference to the accompanying drawings.
FIG. 34 is an exploded perspective view of the conventional non-contact position sensor, and FIG. 35 is a sectioned side view of the same non-contact position sensor.
The conventional non-contact position sensor comprises a first magnetic body 2 having a magnet 1 attached to it, and a second magnetic body 3 disposed to a position where one-side arm 3a confronts one-side arm 2a of the first magnetic body 2. A magnetic sensor element 4 is disposed to a side surface of the magnetic body 3 in a position to confront the magnet 1. A case 5 made of resin encases the magnet 1, the magnetic body 2, the magnetic body 3, and the magnetic sensor element 4 in it, and it also has a connector unit 6. An end of a connector terminal 7 is connected electrically with a lead terminal 8 wired from the magnetic sensor element 4. A cover 9 made of resin closes an opening of the case 5.
The conventional non-contact position sensor constructed as above operates in a manner which will be described next.
The above-described conventional non-contact position sensor has a magnetic flux shutter 10b inserted in a gap where the one-side arm 2a of the magnetic body 2 and the one-side arm 3a of the magnetic body 3 confront with each other, through another gap where the magnet 1 and the magnetic sensor element 4 confront with each other, as shown in FIG. 35. The magnetic flux shutter 10b is mounted to a rotary shaft of an object to be detected (not show in the figure), and it rotates conjunctly with a member 10a under measurement. As the magnetic flux shutter 10b moves in its circumferential direction, magnetic flux of the magnet 1 that reaches the magnetic sensor element 4 changes its density. This change of density of the magnetic flux is output as an output signal by the magnetic sensor element 4, and the output signal is then output to a computer or the like through the lead terminal 8 and the connector terminal 7, to detect a rotating angle of the member 10a under measurement.
In the above structure of the prior art, the magnetic flux shutter 10b is inserted in the gap between the one-side arm 2a of the magnetic body 2 and the one-side arm 3a of the magnetic body 3, and another gap between the magnet 1 and the magnetic sensor element 4. Therefore, a depth of insertion in the gap of the magnetic flux shutter 10b mounted to an end of the rotary shaft 10a changes substantially if the rotary shaft shifts off the center. In the above non-contact position sensor in which the magnetic flux to the magnetic sensor element 4 is turned on and off with the magnetic flux shutter 10b, there exists a problem that rotating angle of the rotary shaft is not detected accurately if the depth of insertion changes so greatly.
Moreover, because the conventional non-contact position sensor has the structure that the magnetic flux shutter 10b is attached in a vertical direction to the distal end of the rotary shaft, it is structurally complicated. Furthermore, in order to mount the non-contact position sensor accurately to the object to be detected, both of them need to be joined closely with respect to each other. There existed a problem, however, that the non-contact position sensor is not easily mountable to the close vicinity of the object to be detected due to the presence of the magnetic flux shutter.
In addition, there was also a problem with the foregoing structure that it exhibits hysteresis in the output characteristic, because of the structure in which the magnetic flux shutter 10b rotates while being inserted between the magnet 1 and the magnetic sensor element 4. That is, electromagnetic induction occurs in the magnetic flux shutter 10b by the lines of magnetic force of the magnet 1. As a result, the magnetic flux shutter 10b is magnetized with N-pole when the magnetic flux shutter 10b rotates in the normal direction, as shown in FIG. 36(a). On the contrary, the magnetic flux shutter 10b is magnetized with S-pole, as shown in FIG. 36(b), when the magnetic flux shutter 10b rotates in the reverse direction. For this reason, there occurs a variation in the lines of magnetic force that affects the magnetic sensor element 4 depending on rotating direction of the magnetic flux shutter 10b. Hence, the hysteresis occurs in the output characteristic, as the output varies between the normal direction and the reverse direction in which the member 10a under measurement rotates.
An object of the present invention is to solve the foregoing problems of the prior art, and to provide a non-contact position sensor that realizes a substantial reduction in amount of deviation of the rotary shaft of the object to be detected even if the rotary shaft of the object to be detected shifts off the center, so as to achieve accurate measurement of the rotating angle. The non-contact position sensor also facilitates mounting of it to the object to be detected with both of them joined closely together.
Another object of the invention is to provide a non-contact position sensor of an improved characteristic that obviates hysteresis in the output signals due to rotation in the normal direction and the reverse direction of the object being detected between.
In addition, still another object of the invention is to provide a non-contact position sensor having an outstanding linearity in the output.